Essential Chemistry Concepts and Formulas

Chemical Reactions

Types of Chemical Reactions

• Synthesis: A + B → AB
• Decomposition: AB → A + B
• Single Displacement: A + BC → AC + B
• Double Displacement: AB + CD → AD + CB
• Combustion: A + O₂ → H₂O + CO₂ (typically for hydrocarbons)
• Acid-Base: Acid + Base → Salt + Water
• Precipitation: Soluble Salt A + Soluble Salt B → Precipitate + Soluble Salt C

Stoichiometry and Mole Concepts

Key Stoichiometry Relationships

• Mass: 1 mole = Molar Mass (in grams)
• Volume: 1 mole = 22.4 L @ STP (Standard Temperature and Pressure)
• Particles: 1 mole = 6.022 × 10²³ particles (Avogadro's Number)
• Mole-Mole Conversions: Use coefficients from a balanced chemical equation.

Standard Temperature and Pressure (STP)

• Temperature: 0 °C (273.15 K)
• Pressure: 1 atm

Gas Laws and Ideal Gas Equation

Temperature Conversion

• Celsius to Kelvin: K = °C + 273.15

Fundamental Gas Laws

• Boyle's Law: P₁V₁ = P₂V₂ (Constant T, n)
• Charles's Law: V₁/T₁ = V₂/T₂ (Constant P, n)
• Gay-Lussac's Law: P₁/T₁ = P₂/T₂ (Constant V, n)
• Avogadro's Law: n₁/V₁ = n₂/V₂ (Constant P, T)
• Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂ (Constant n)
• Ideal Gas Law: PV = nRT (where R = 0.0821 L·atm/(mol·K))

Chemical Bonding and Naming Conventions

Electron Configuration

The order of filling atomic orbitals:

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², 4f¹⁴, 5d¹⁰, 6p⁶, 7s², 5f¹⁴, 6d¹⁰, 7p⁶, 8s²

Common Polyatomic Ions

• Sulfate: SO₄²⁻
• Hydroxide: OH⁻
• Nitrate: NO₃⁻
• Ammonium: NH₄⁺
• Acetate: CH₃COO⁻
• Sulfite: SO₃²⁻
• Phosphate: PO₄³⁻
• Carbonate: CO₃²⁻
• Chlorate: ClO₃⁻
• Chlorite: ClO₂⁻
• Nitrite: NO₂⁻
• Phosphite: PO₃³⁻

Naming Compounds

General Rules

• The first element in a compound is typically positive, and the second is negative.

Cations

• Metals/metalloids that lose electrons.
• Example: Na⁺ = Sodium ion
• Transition metals that can form multiple ions with different charges use Roman numerals to indicate the charge (e.g., Iron(II) Oxide).

Anions

• Nonmetals/metalloids that gain electrons.
• Example: O²⁻ = Oxide
• Suffixes:
  • -ide: Typically for monatomic nonmetal ions (e.g., chloride, oxide).
  • -ate, -ite: Used for polyatomic ions containing oxygen (e.g., sulfate, sulfite).

Covalent Compounds (between two nonmetals)

• Use prefixes to indicate the number of atoms: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca-, dodeca-.
• First Element: Add prefix (mono- is usually omitted for the first element).
• Second Element: Add prefix and change the ending to -ide.
• These compounds involve shared electrons.

Ionic Compounds (between a metal and a nonmetal/polyatomic ion)

• Cations with variable charges (transition metals) require Roman numerals.
• Example:
  • FeO: Iron(II) Oxide (Fe is 2+)
  • Fe₂O₃: Iron(III) Oxide (Fe is 3+)

Common Diatomic and Polyatomic Elements

• P₄ (Tetraphosphorus)
• Br₂ (Bromine)
• I₂ (Iodine)
• N₂ (Nitrogen)
• Cl₂ (Chlorine)
• H₂ (Hydrogen)
• O₂ (Oxygen)
• F₂ (Fluorine)

Fundamental Chemistry Principles

Law of Conservation of Mass

Atoms cannot be divided, created, or destroyed in a chemical reaction.

Significant Figures Rules

1. All non-zero digits are significant.
2. Zeros between non-zero digits are significant.
3. Zeros to the right of the decimal point AND to the right of a non-zero digit are significant.
4. Zeros to the left of all non-zero digits (leading zeros) are not significant.
5. Zeros to the right of all non-zero digits but to the left of an implied decimal point may or may not be significant (e.g., 100 could have 1, 2, or 3 sig figs; use scientific notation for clarity).

Thermodynamics Basics

Phase Changes

• Solid to Gas: Sublimation
• Gas to Solid: Deposition
• Gas to Liquid: Condensation
• Liquid to Gas: Vaporization (or Boiling)
• Liquid to Solid: Freezing
• Solid to Liquid: Melting

Endothermic and Exothermic Reactions

• Endothermic Reactions: Chemical reactions in which reactants absorb heat energy from the surroundings to form products. The system gains energy.
• Exothermic Reactions: Chemical reactions in which energy is released (often as light or heat) to the surroundings. The system loses energy.